Bind to an existing socket connection? No, there is no way, in Perl or any other language to do it.

Well, not any legal means anyway.

What you would have to do is snoop the packets that come in, learn the source/destination port and the sequence number, then spoof a RST packet. For assembling the packet, it looks like NetPacket::IP might be of use, and for snooping, I think Net::Pcap might be just the ticket.